The present invention relates to digital display devices using drums which are actuated by a magnet capable of orientating itself in several stable directions by selective magnetization of the branches of a fixed, grouped magnetic circuit which receives digital information to be displayed.
Indicators of this type, which receive information in analogue form, therefore require an analogue/digital conversion system. The information to be displayed is usually renewed at a constant rate which is compatible with the response time required by the display means (for example, the frequency normally selected is around 2 Hz). However, the analogue/digital converter has a much shorter response time (of the order of 10 ms, for example, for a double track type system). An extra so-called "sequencing device" which produces conversion and store instructions for the calculated value at the selected renewal frequency is therefore added. The addition of these devices gives rise to a certain number of defects with regard to the display. In fact, even if the input information is perfectly stable, this display is not necessarily stable and would only be so as the result of the error introduced by the converter. Thus, the lowest digit can be seen to develop at the renewal rate, particularly if the input information is evolutionary and if this evolution takes place at a rate which is higher than the rate compatible with the renewal frequency. The numerical values displayed successively can be very far apart and, consequently, the directions of rotation of the different drums are neither constant nor in harmony with the input information. In other words, the display provided by drums does not give any indication of the "tendency" of the input in this case.
In order to overcome this disadvantage, a device forming the subject of the invention proposes to control the analogue/digital converter by means of a signal which is a function of the information to be displayed by making the frequency at which the display of the said information is renewed variable and/or a function of its rate of change. To do this, the circuit emitting the input information is connected to the input of both the analogue/digital converter and a differentiating circuit capable of performing the differentiation of the input quantity relative to time, the output of which is connected to a circuit containing means for comparing voltages and/or frequencies, means for producing frequencies and means for controlling the analogue/digital converter and/or all or a proportion of the display drums.